Block copolymers comprising terminal poly(styrene) blocks and one or more central poly(isoprene) blocks, more particularly triblock copolymers, are used in hot-melt adhesive compositions for the manufacture of disposable articles. More specifically triblock copolymers having a poly(styrene) content of from 25 weight percent (wt. %) to 35 wt. % and having a total apparent molecular weight of from 100,000 Daltons (Da or grams/mole (g/mol)) to 300,000 Da are generally used in hot-melt adhesive compositions in the diaper industry in two manners:                1) as assembly adhesive to glue the diaper poly(ethylene) main frame, and        2) as an attachment adhesive to glue the elastic threads (fibers) or films which are used as waist and leg bands.        
Suitable adhesives are characteristically clear or lightly colored, low in odor, sprayable as a hot-melt adhesive, show good adhesion to poly(olefin) films and do not strike through the non-woven back sheet. These adhesives also typically display a melt viscosity that allows spray application typically in the temperature range of 160° C. to 180° C. Also another desirable quality of these adhesives is that they are relatively inexpensive.
Elastic attachment adhesive is used to adhere elastic threads to polyethylene and non-woven films in order to form an elastic waist or leg band for diaper or hygiene products. Multiple strands of elastic threads are elongated, commonly 300%, and coated with adhesive composition at a temperature of about 160° C. to 180° C. just prior to being pinched inside of the poly(olefin) and non-woven films. Like construction adhesives, they are usually sprayed in a variety of patterns such as spiral or wrap-around patterns. When the ends of the elastic are cut later in the process, the composite contracts causing the non-woven and poly(olefin) films to pucker to form an elastic band.
Although specifically designed block copolymers show an acceptable hot-melt viscosity/temperature profile and have a sufficiently low viscosity at the usually applied hot-melt temperatures of up to 180° C. thereby enabling efficient processing, there is still an economic need for block copolymers which demonstrate processing efficiency, in combination with other attractive properties noted hereinbefore.
The physical requirements for an elastic attachment adhesive are:                1) high cohesive strength and good creep resistance;        2) ability to adhere strongly to polyethylene and polypropylene non-woven films in addition to more polar elastic like polyurethane;        3) low melt viscosity and consequently a high melt flow rate—low temperature application typically requires a viscosity range of about 10,000 centipoise (cps) to 15,000 cps at spray nozzle temperature;        4) sufficient melt viscosity balanced against maintaining sufficient pump pressure; and        5) high melt strength for spray applications.        
It will be appreciated that a relatively low hot-melt viscosity facilitates a high production speed in a diaper manufacturing line without the production of significant amounts of off specification product. Problems which normally cause such off specification product may be, for example, adhesive viscosity degradation, adhesive discoloration, damage to the polyethylene film or formation of char. Accordingly, developmental efforts in diaper manufacture continue today with down-gauging of polyolefin films and elastic threads which require a spray application temperature as low as possible while still maintaining adequate adhesion and creep resistance
The present disclosure provides improved adhesive compositions which show a reasonable viscosity at temperatures in the range of from about 125° C. to about 140° C. in order to avoid the hereinbefore mentioned problems while allowing sprayability at higher production speeds.